Problem in reading RDF url in C#

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C#5.0

RDF

i am trying to read triples of pizza ontology using uri http://www.dcs.bbk.ac.uk/~michael/sw/slides/pizza.owl

code is:

private void button2_Click(object sender, EventArgs e)
       {
           try
           {
               IGraph g = new Graph();


            UriLoader.Load(g, new Uri("http://www.dcs.bbk.ac.uk/~michael/sw/slides/pizza.owl"));
           }
           catch (RdfParseException parseEx)
           {
               //This indicates a parser error e.g unexpected character, premature end of input, invalid syntax etc.
                //parseEx.Message);
               textBox1.Text = parseEx.Message;
           }
           catch (RdfException rdfEx)
           {
               //This represents a RDF error e.g. illegal triple for the given syntax, undefined namespace
               //Console.WriteLine("RDF Error");
               textBox1.Text =  rdfEx.Message;
           }
       }

But when i am running this code i am getting this error



ERROR: [Line 1 Column 6] Spaces are not valid in URIs

i dnt undrstand this. pls help me.